A power struggle exists within the guild between rogues "D" and "K." This quest is the culmination of "K"s quest line, he asks for the warden's help betraying "D" to the guards.
First all of "K's" friends must be given a signal. Gorim and Sister Theohild in the Denerim market, and the tranquil proprietor of the Wonders of Thedas. Talk to each and given them "K's" wink and nod and they will return the signal as expected. After all the signal have been sent the plan check in with "K's" Denerim guard contact in the market. He will tell you to watch your back while traveling in Denerim. While traveling in Denerin you will have a random encounter with "D's" men, kill the Lieutenant to reveal the location of "D's" hideout.